The present invention relates generally to illumination, and more particularly to producing circular or semicircular emission with in an equatorial-type solid angle.
Numerous illumination situations require lighting devices that emit a planar 360° pattern, like a time-exposure picture of a lighthouse-beam sweeping around the horizon. U.S. Pat. No. 6,473,554, by Pelka and Popovich, incorporated herein by reference, utilizes a conicoid figure of revolution situated just over an LED light source, with the axis of revolution in a vertical direction. This cuspated reflector laterally deflects the rays going upward from the source, by internal reflection within a dielectric material. Similar configurations in metallic reflectors have been known for far longer. The principal characteristic of this approach is its aspect ratio, with device diameter two or more times device thickness. This is advantageous in applications where devices height must be minimized. In other situations, however, horizontal size must be minimized, such as with LEDs on a circuit board. Also, for light-injection such devices must be surrounded by the waveguide, since a less-than-360° emission-pattern wastes light.
A 180° emission pattern, however, is desirable, for injection into the edge of a waveguide. Doing this in accordance with the prior devices and/or methods would throw away half the light.